A fuel cell is an electric power generation system that generates electrical energy through a chemical reaction of oxygen and hydrogen contained in a hydrocarbon-based material such as methanol, ethanol, or natural gas
Fuel cells can be classified as phosphoric acid type, molten carbonate type, solid oxide type, polymer electrolyte type, or alkaline type, depending on the kind of electrolyte used. Although each fuel cell basically operates in accordance with the same principles, the kind of fuel, the operating temperature, the catalyst, and the electrolyte may be selected depending upon the type of fuel cell.
Recently, polymer electrolyte membrane fuel cells (PEMFCs) have been developed with power characteristics superior to those of conventional fuel cells, lower operating temperatures, and faster starting and response characteristics. PEMFCs have advantages in that they can be applied to wide fields such as for portable electrical power sources for automobiles, for distributed power sources such as for houses and public buildings, and for small electrical power sources for electronic devices.
A polymer electrolyte fuel cell is essentially composed of a stack, a reformer, a fuel tank, and a fuel pump. The fuel pump provides the fuel stored in the fuel tank to the reformer. The reformer reforms the fuel to generate the hydrogen gas and supplies the hydrogen gas to the stack. The stack forms the body of the polymer electrolyte fuel cell and is where the hydrogen is electrochemically reacted with oxygen to generate the electrical energy.
In a direct methanol fuel cell (DMFC), liquid methanol fuel is directly introduced to the stack. Consequently, the direct methanol fuel cell can omit the reformer which is essential for the polymer electrolyte fuel cell.
According to the above-mentioned fuel cell system, the stack generally includes several or several tens of unit cells consisting of a membrane electrode assembly (MEA) and a separator (or referred to as a “bipolar plate”) laminated together. The membrane electrode assembly is composed of an anode (referred to as a “fuel electrode” or “oxidation electrode”) and a cathode (referred to as an “air electrode” or “reduction electrode”) separated by the polymer electrolyte membrane.
The performance of a fuel cell depends on the electrode which participates in the electrochemical oxidation and reduction reactions, and therefore, research is being undertaken for improvements of the electrode.